1. Field of the Invention
The present invention relates to a centrifugal fan, and particularly, to a thin high-power centrifugal fan.
2. Description of the Related Art
FIG. 23 is a perspective view illustrating an example of a related-art centrifugal fan. FIG. 24 is a sectional side view illustrating the example of the related-art centrifugal fan.
As shown in FIGS. 23 and 24, a centrifugal fan 801 is generally configured by installing an impeller 830 in a casing 810 having an inlet 813 (833) and an outlet 819. The impeller 830 includes a plurality of blades 851 arranged around a rotating shaft of a motor 860. The centrifugal fan 801 suctions air from the inlet 813 (833), makes the air flow through the blades (wings) from the center of the impeller 830, and expels the air outward in the radial direction of the impeller 830 by a fluid force due to a centrifugal action according to rotation of the impeller 830. The air expelled outward from the outer circumference of the impeller 830 is discharged from the outlet 819 of the casing 810.
As shown in FIG. 24, the centrifugal fan 801 is thin. The centrifugal fan 801 has the motor 860 provided at the substantially center portion of the casing 810 in order for rotating the impeller 830. The motor 860 is an outer rotor type brushless motor disposed such that its rotor yoke 863 is fit in the impeller 830.
This centrifugal fan 801 is widely used for cooling, ventilation, and air-conditioning of appliances, office automation equipment, and industrial equipment, blowers for vehicles, etc. The blowing performance and noise of the centrifugal fan 801 are greatly affected by the wing (blade) shape of the impeller 830 and the shape of the casing 810 (the structure of the centrifugal fan 801).
Incidentally, in order to reduce noise or to improve blowing performance, it has been performed to optimize the shapes of impellers or the structures of casings, and various proposals have been made.
For example, JP-A-UM-H5-12692 discloses a turbo fan in which lengthwise recesses or circular recesses are formed on the pressure surface sides of blades, such that fan efficiency is improved.
JP-A-UM-S64-19100 discloses a multi-blade fan in which grooves are formed in the longitudinal directions of blades on the positive pressure surface sides of the blades, such that blade efficiency is improved.
JP-A-2006-9577 discloses a multi-blade fan in which stepped parts are formed such that the thickness of each blade decreases from the leading edge toward the trailing edge, whereby the noise of an impeller is reduced.
JP-A-UM-S63-160400 discloses a sirocco fan in which unevenness is formed on the upstream side of the pressure surface side of each blade, such that the operating efficiency of the main body of the fan is improved and noise is reduced.
With the progress of size reduction, thickness reduction, high-density mounting, and energy-saving of various apparatuses, it has been always required to improve the efficiency of a centrifugal fan to be mounted on those apparatuses.
At the same time, it has been always required to further reduce the level of noise generated by driving of a centrifugal fan.